Summary: Apolipoprotein E (APOE) has been one of the most studied genes in longevity since Schacter et al. in 1994 showed that French centenarians have a low frequency of the ?4 allele and an increased frequency of the ?2 allele. While the mechanism of the demographic selection of the ?4 allele appears related to its association with Alzheimer?s disease and vascular disease, several underpowered studies have produced conflicting results about ?2?? role in longevity and Alzheimer?s disease. For this project, we have assembled genotype data of APOE alleles in 13,060 individuals, including 2,145 individuals who meet the following definition of exceptional longevity (EL): surviving to ages beyond the oldest 1% of individuals from the 1900 birth year cohort (age 96 and older for men, and 100 and older for women). We achieved this substantial sample size by pooling data from 4 studies of longevity: The New England Centenarian Study, the Long Life Family study, the Southern Italian Centenarian Study, and the Longenity Project of Ashkenazi Jewish centenarians. In collaboration with Novartis, we generated a proteomic dataset of 5,000 proteins in serum samples of 230 New England Centenarian Study participants (ages 50 to 119 years). We propose to use this unique data set, and genotype and gene expression data from 6 additional studies to investigate the association of the ?2 allele with survival free of, or with delayed cognitive impairment, Alzheimer?s, and related dementia. Specifically, we propose to conduct a series of statistical and bioinformatics analyses to test the hypotheses: (i) Is the ?2 allele associated with escaping and/or delaying Alzheimer?s disease and related dementia? (ii) What are the associated mechanisms of action? (iii) Are there known compounds that could mimic the molecular environment associated with the ?2 allele? We will answer these questions in two specific aims. In Aim 1, we will use APOE genotype data to investigate the association between the ?2 allele and prevalence and incidence of Alzheimer?s disease. We will extend this analysis to age at death as a quantitative trait and ages of onset of dementia and Alzheimer?s disease, cardiovascular disease, stroke, as well as rate of cognitive decline. We will collaborate with the Japanese Centenarian Study and the Danish Aging Study to replicate associations, in addition to using data from the Health and Retirement Study. In Aim 2, we will begin translating the results from the human genetic studies in Aim 1 by constructing APOE genotype-specific molecular signatures based on plasma proteins and multi-tissue gene expression data. We will query repositories such us the Connectivity Map for expression signatures of biomolecules, compounds and drugs that match the molecular signatures associated with APOE alleles in order to discover their activating compounds. We will use causal inference methods including mediation analysis and Mendelian randomization to investigate the joint effect of the ?2 allele and molecular signatures on age of onset of Alzheimer?s disease, dementia, cardiovascular disease, stroke, and rate of cognitive decline. This R21 will discover molecular mechanisms underlying the ?2 allele?s associated survival advantage and possibly open new directions for healthy aging therapeutics.